1. Technical Field
The present invention relates to an electrophotographic photoconductor used in an image forming method of an electrophotographic system and to an image forming apparatus provided with the electrophotographic photoconductor.
2. Description of Related Arts
In recent years, image forming apparatuses such as electrophotographic copiers and printers have been required to have higher image quality. Specific examples of requirements for high quality include improvement in image uneven density on individual pages or between pages. In image forming apparatuses, detectability has been improved, accompanied with increased quality and resolution of images formed, and the improvement leads to increased occurrence of image uneven density. In order to improve uneven density in image forming apparatuses, various attempts have conventionally been made but further research is still underway.
Recently, an electrophotographic photoconductor (hereinafter referred to also simply as “photoconductor”) having a laminated structure which is negatively charged has been used widely. In the photoconductor, usually, an intermediate layer and a photosensitive layer that includes a charge generation layer and a charge transport layer formed thereon are laminated on an electrically conductive support. In the electrophotographic photoconductor having such a negatively charged type laminated structure, When the surface is negatively charged and thereafter exposed to light, the charge generation layer generates charges, of which negative charges (electrons) move to the electrically conductive support through the intermediate layer, whereas positive charges (positive holes) move to the surface of the electrophotographic photoconductor through the charge transport layer to cancel negative charges on the surface thereof, thereby forming an electrostatic latent image. Thus, it is desired that the intermediate layer has electron transport property (to allow electrons generated in the charge generation layer to rapidly move to the electrically conductive support) and positive-hole blocking property (to suppress the injection of positive holes from the electrically conductive support to the photosensitive layer).
For achievement of such functions in an intermediate layer, there are known techniques of using an intermediate layer that includes specific metal oxide particles. The techniques have attempted to improve the functions of an intermediate layer and reduce image defects such as uneven density.
For example, as a conventional attempt to reduce image defects, a following conventional technique is known: an under coat layer is composed of titanium oxide particles surface-treated with methyl hydrogen polysiloxane and a photosensitive layer includes titanyl phthalocyanine as a charge generation layer (see Patent Literature 1 below). Patent Literature 1 has reported that the uses of the titanium oxide particles subjected to the specific surface treatment and the specific charge generating material could improve image characteristics and electrical characteristics and could enhance the preservation stability of dispersion liquid, particularly under environments ranging from high temperature with high humidity to low temperature with low humidity.
As another attempt to reduce image defects such as fogging under high temperature and high humidity conditions, there is known a conventional technique in which a titanium oxide-containing intermediate layer is controlled to be in a specific range of reflection absorbance (see Patent Literature 2 below). Patent Literature 2 has described use of titanium oxide coated with an organic silicon compound, thereby water-absorbing properties and dispersibility of titanium oxide were improved.
As another attempt of conventional art to reduce image defects such as fogging and black spots, a following electrophotographic photoconductor is known: an intermediate layer is formed by including n-type semiconductor fine particles and a binder resin, where the n-type semiconductor fine particles are surface-treated a plurality of number of times and the final surface treatment is performed by using a reactive organic silicon compound (see Patent Literature 3 below).    Patent Literature 1: Japanese Laid-Open Patent Publication No. 2005-134924    Patent Literature 2: Japanese Laid-Open Patent Publication No. 2007-094226    Patent Literature 3: Japanese Laid-Open Patent Publication No. 2002-236381